Aluminum base alloy



Patented June 16, 1942 UNITED STATES PATENT OFFICE r ALUMiNUM BASE ALLOY Louis W. Kemp! and Walter A. Dean, Lakewood, Ohio, assignors to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application December 30, 1941, Serial No. 424,893

2 Claims. (01. 75-446) tures has been increased by the demand for more powerful motors for aircraft.

It is an object of this invention to provide an alloy composition which exhibits high strength and resistance to deformation at elevated temperatures, especially at the higher temperatures found in the newer aircraft motors. A particular object is to provide an alloy which possesses a high thermal conductivity along with the high strength at elevated temperatures. Still another object is to provide an aluminum base alloy having a higher modulus of elasticity than the common aluminum base alloys now in use.

' We have discovered that an aluminum base alloy containing from about 20 to 40 per cent beryllium, from 0.25 to 3 per cent magnesium, from 2 to 15 per cent zinc, and the balance substantially aluminum possesses the aforementioned properties. More particularly, we have found that some of the alloys within this range possess tensile strengths at elevated temperatures which are considerably greater than thatof alloys heretofore used for such service. The presence of zinc in the alloys increases their susceptibility to improvement in strength, solution heat treatment and age hardening as compared to the same alloys without zinc. Furthermore, this increase in strength is accompanied by a lower density than aluminum, a relatively high thermal conductivity, and a high modulus of elasticity. This combination of properties, espefrom alloys having lower modulus values. Our alloys may be used in either cast or wrought form but we prefer to use them in wrought form.

The tensile properties at an elevated temperature of some examples of our alloys, and the thermal conductivity at room temperature of two of these alloys, together with the correspondin properties of certain well knownaluminum base alloys which have been used heretofore for high temperature service, are given in Table I below. The first of the two alloys which contained no beryllium, i. e. the Al-Cu-Ni-Mg alloy, may be considered as being typical of aluminum base alloys designed for service at elevated temperatures. The balance of the composition of each of the alloys appearing in the tables was aluminum and the usual impurities. The beryllium-containing alloys were cast as ingots and extruded into the form of rods.

The thermal conductivity and tensile property determinations were made on specimens taken from extruded rods while the test specimens of the other aluminum base alloys were taken from forged rods. The difference in fabricating practices used in making the rods is considered to have no significant effect upon the test results reported here. The specimens without beryllium received the conventional solution heat treatment and artificial aging before being subjected to any of the treatments and tests herein described in order to duplicate the condition of the alloys in many commercial applications. Specimens of the last beryllium-containing alloy in TableI likewise received a solution heat treatment and artificial aging. All of the test bars for tensile strength determinations were subjected to a short time test at elevated temperacially that of high strength, and relatively high tures consisting of first stabilizing them by heating them for 16 'hours at 700 F. This preliminary treatment served to accelerate any changes which would have occurred on exposure. to a lower temperature over a long period of time.

We have found from a number of other tests that-such preliminary stabilizing treatment for a relatively short period of time at a temperature higher than encountered in serviceaflects properties to a comparable extent as more extended periods at the temperature of service operation. Following the preliminary stabilizing treatment, the bars for tensile strength determinations were cooled to. room temperature, then reheated to the testing temperature; in this case 600 F., held at this temperature for one-half hour, and then broken in tension at 600 F. in the usual manner.

The thermal conductivity values were calculated from electrical resistivity measurements made at room temperature. The calculations were based on the well recognized Wiedemann- Franz-Lorenz relationship between the thermal conductivity and electrical resistivity of metals.

It is generally true that there is such a small change in thermal conductivity of aluminum base alloys over the range of room temperature to about 600 F. that values at room temperature are very close to those at elevated temperaturessuch as exist in internal combustion engines. The test specimens for electrical resistivitymeasurements were in the same temper as thatof the specimens used for tensile tests prior to the stabilizing treatment.

-TABLE I Tensile properties at 600 F. and thermal conductivity at room temperature Alloy composition Thermal Tensile Elongation conductivity strength in 2 inches G S. Be Mg Zn Ni Si units) Percent Percent Percent Percent Percent Zita/sq in Percent 24.15 0. 56 5. 21 8,600 17 0.38 24.09 0. 63 9. 97 8, 200 14 39. 41 0. ll. 10, 000 8 0. 32 28. 65 0.87 3. 43 13,900 8. 5 0. 5 4.0 6,000 75 0. 37 1. 0 o. 9 5,600 5;; 0. 32

It will be noted that the tensile strength of the beryllium-containing alloys at the elevated temperature exceeds that of the two aluminium base compositions used for comparison. The lower elongation. values of the berylliumalloys also indicate a greater resistance to deformation at elevated-temperatures. These tensile properties therefore indicate that these alloys are much better adapted for service at such high temperatures as 600 F. than the other two aluminum base alloys which have been employedheretofore for that purpose. It is also to be observed that the thermal conductivities of the alloys containing 24.15 and 29.41 per cent beryllium are substantially the same as those of the two alloys containing no beryllium. A thermal conductivity of 0.3 c. g. s. units, or more, is considered to be -relatively high for alloys used at elevated temperatures.

Modulus of elasticity determinations were made at room temperature on two alloys contain- TABLE II Modulus of elasticity at room temperature Alloy composition Modulus Be Mg Zn Cu Mn Ni Si Per- Per- Per- Per- Per- Per- Per- Lba/eg. in. cent cent cent4 cent cent cent cent The superiority of the beryllium-containing alloy over the other alloys is readily apparent temperature properties described above.

has been found to be necessary to obtain such a combination of properties, but that if more than 40 per cent is employed, the alloy becomes very dimcult to work. The presence of magnesium in the alloy considerably enhances the strength and resistance to fatigue at elevated temperatures. We have found that at least 0.25 per cent magnesium is necessary to achieve this purpose, while on the other hand, if more than 3 percent is used, fabricating difliculties are encountered. The addition of zinc serves to increase the susceptibility of the alloys to improvement in strength by solution heat treatment and age hardening as compared to the same alloys without zinc, and the greatest benefit in this respect is obtained by using from 2 to 15 per cent of this element. Alloys which contain from 22 to 30 per cent beryllium, 0.5 to 1.5 per cent magnesium, and 2.5 to 10 per cent zinc are preferred because they possess the most satisfactory com-- binatlon of strength and workability.

The expression balance substantially aluminum, as used hereinabove and in the appended claims, means that small amounts of the usual impurities as well as'other elements may be present in the alloys without affecting the high The presence of any elements which substantially impair the strength and thermal conductivity properties of these alloys at elevated temperatures are therefore excluded from the scope of this invention.

In referring to certain properties of our alloys at. elevated temperatures we mean that these properties are particularly outstanding in the range of 400 to 600 F., however, the advantageous properties of our alloys are not confined to that temperature range.

We claim: 1. An aluminum basealloy consisting of from about 20 to 40 per cent beryllium, 0.25 to 3 per cent magnesium, 2 to 15 per cent zinc. and the balance substantially aluminum, said alloy being characterized by a high tensile strength at at elevated temperatures consisting of from 22 to 30 per cent beryllium, 0.5 to 1.5 per cent mag-'- nesium, 2.5 to 10 per cent zinc, and the balance substantially aluminum, said alloy being characterized by a high tensile strength at elevated temperatures combined with a relatively high thermal conductivity, and a greater susceptibility ,to improvement in strength by solution heat treatment and age hardening than the same alloy LOUIS-W. K M F. WALTER A. DEAN.

l0 devoid oi zinc.

CERTIFICATE OF coi'umcnon'. Pateht No. 2,286,626. June16, 1912.

LOUIS w. KEHPF, ET AL.

It is hereby certified that errorapp e ers in the printed a'pecific'aflon of the above numbered patent. requiring correction as -1-'ol 1owa: Page Table I, first column thereof, for 9.1m" read 29.h1--; and same page,

first 001m, line 32; for "aluminium" r'eald a1uminumend tha'tthe eaid Letters Patent should be read with this correction therein that the" same may eonfonh to the recoi -d of the case innthe Patent Office.

Signed and .sealed this day ef'August, A. D. 1911.2.

I .7 Henry van-3am, '(seal') I A cting'comiuioner of Patents. 

